Gravity based patient image orientation detection

ABSTRACT

The present teachings generally provide for a surgical navigation system for use with an x-ray imaging device. The x-ray imaging device acquires x-ray images of an anatomical structure of interest at an angular position. The surgical navigation system includes a localizer with a tracking sensor, a gravity vector sensor coupled to the tracking sensor, a tracking device configured to be coupled to the C-arm so as to be movable with the C-arm between a plurality of angular positions. The tracking device comprises a tracking element detectable by the tracking sensor. A computer processor is operatively coupled with the localizer and configured to implement an imaging routine that receives tracking data from the tracking sensor and a gravity vector from the gravity vector sensor, generating an image vector indicative of the angular position at which the x-ray image was acquired.

BACKGROUND

Navigation systems for tracking the position of one or more work targetslocated inside a body, either alone or in relation to one or morevarious working instruments, are used in many types of applications. Oneapplication in which navigation systems are commonly used is in thefield of navigated surgical procedures. In this field, surgicalnavigation systems are now commonly used to assist in planning asurgical procedure or executing a planned surgical procedure, so as toimprove the accuracy of the surgical procedure and minimize theinvasiveness thereof.

It is common for surgical navigation systems to use X-ray imagingsystems. The X-ray imaging systems typically uses a C-arm configuration.The C-arm includes a C-shaped recording unit on an adjustable andmoveable mounting structure opposite an x-ray source. Typically, thex-ray source is mounted on one end of the C-arm, and the imaging portionis mounted opposite of the x-ray source on the other end of the C-arm.The C-arm is positioned around an object to be imaged, such as ananatomical feature of a patient, and an image is taken in a firstposition. The C-arm may then be moved into another position to acquireanother image of the same anatomical feature from a different viewpoint.Of particular interest in surgical procedures are lateral andanterior-posterior (A-P) views. Known systems require a surgeon or othermember of the surgery team to manually correlate the lateral and A-Pviews, for example, on a user interface for the system to properlyutilize the images. For example, the first image is taken in a firstposition or view (e.g., a lateral view) and when a second or subsequentimage is taken in a second position or view (e.g., anterior-posteriorview), a surgery team member would have to manually switch the displayto show the newly acquired second/subsequent image from the first image.

Typically, x-ray images are taken for visual navigation systems in alateral pose and an anterior-posterior pose for locating the anatomicalfeature and for developing a pair of 2D representative images which thenhave surgical instrument representations overlaid for intra-operativetracking. Visual navigation systems use imagine based navigation frompreoperative and intraoperative images along with some form of patienttracker. Visual navigation is used primarily with cranial, spine, andENT procedures. The images can be aligned with a model in the navigationsystem to provide intraoperative positions of the anatomical features ofinterest.

Although fluoroscopy is common in surgical navigation systems forpre-operative, and intraoperative applications, it would be attractiveto have a surgical navigation system which automatically recognized theposition the C-arm is in when an image is take, increasing workflowefficiency.

SUMMARY

The present teachings generally provide for a surgical navigation systemfor use with an x-ray imaging device. The x-ray imaging device may beconfigured to acquire x-ray images of an anatomical structure ofinterest at one of a plurality of angular positions relative to adirection toward center of Earth gravity. The surgical navigation systemmay comprise a localizer with a tracking sensor, and a gravity vectorsensor coupled to the tracking sensor. The gravity vector sensor may beconfigured to detect the direction toward center of Earth gravityregardless of an orientation of the tracking sensor. The surgicalnavigation system may further include a tracking device configured to becoupled to the C-arm imaging device so as to be movable with movement ofthe C-arm imaging device between the plurality of angular positions. Thetracking device may comprise a tracking element detectable by thetracking sensor. The surgical navigation system may include a computerprocessor operatively coupled to the localizer. The computer processormay be configured to implement an imaging routine. The imaging routinemay operate by receiving tracking data from the tracking sensor and agravity vector from the gravity vector sensor, to generate an imagevector based on the tracking data with the image vector being indicativeof the one of the plurality of angular positions at which the x-rayimage was acquired. The computer processor may then determine an anglebetween the image vector and the gravity vector and assigning an imageidentifier to the x-ray image based on the determined angle. The imageidentifier may be configured to provide an indication of the one of theplurality of angular position at which the x-ray image was acquired. Adisplay may be coupled to the computer processor such that the displayis configured to display the x-ray image with the image identifiercorresponding to one of the plurality of angular positions at which thex-ray image was acquired. The computer processor may be configured todisplay a visual representation of a surgical instrument onto the x-rayimage on the display. The visual representation may appear from one ofat least two different perspectives based on the image identifier.

The surgical navigation system may further include a memory coupled tothe computer processor. The computer processor may be configured tostore a first predefined range of angles and a second predefined rangeof angles exclusive from the first predefined range of angles. Theimplementation of the imaging routine by the computer processor mayfurther comprise receiving the first and second predefined ranges ofangles from the memory, determining whether the determined angle iswithin the first predefined range of angles or the second predefinedrange of angles, and assigning the image identifier to the x-ray imagewhen the determined angle is within the first predefined range of anglesand not within the second predefined range of angles. The firstpredefined range of angles may be greater than 45° to less than or equalto 135°, and the second predefined range of angles may be greater than0° to less than or equal to 45°, and greater than 135° to less than orequal to 180°. The image identifier may be a lateral image identifier oran anterior-posterior image identifier configured to be displayed alongwith the x-ray image to provide the indication that the x-ray image is alateral x-ray image of the anatomical structure. The memory may beconfigured to store a plurality of predefined ranges of angles exclusivefrom one another. The image identifier may be a plurality of imageidentifiers. Each of the plurality of image identifiers corresponding toone or more of the plurality of predefined ranges of angles. The imagingroutine may comprise retrieving the predefined ranges of angles from thememory, determining which one of the predefined ranges of angles thedetermined angle is within, and assign one of the plurality of imageidentifiers to the x-ray image based on the determined one predefinedrange of angles. The imaging routine may further comprise updating thex-ray image on the display with a second x-ray image on the display whenthe second x-ray image is assigned a second image identifier the same asthe first image identifier. The second image identifier may be based ona second determined angle between a second image vector being indicativeof one of the plurality of angular positions at which the second x-rayimage was acquired, and the gravity vector.

The teachings further provide for a method for acquiring an x-ray imageof an anatomical structure with a C-arm imaging device and identifyingthe x-ray image on a display. A navigation system may be providedincluding a tracking device coupled to the C-arm imaging device andincluding a tracking element detectable by a tracking sensor of alocalizer, a gravity vector sensor configured to detect the directiontoward center of Earth gravity regardless of an orientation of thetracking sensor, and a computer processor. The method may compriseacquiring a first of the x-ray images with the C-arm imaging device at afirst angular position. The tracking sensor may detect a first pose ofthe tracking device as the first x-ray image is acquired. The computerprocessor may generate a first image vector based on the first pose ofthe tracking device and a gravity vector based on the gravity vectorsensor. The computer processor may determine a first angle between thefirst image vector and the gravity vector. The computer processor mayassign a first image identifier to the first x-ray image based on thefirst determined angle and displaying the first x-ray image on thedisplay. The C-arm imaging device may acquire a second of the x-rayimages at a second angular position different than the first angularposition. The tracking sensor may detect a second pose of the trackingdevice as the second x-ray image is acquired. The computer processor maygenerate a second image vector based on the second pose of the trackingdevice. The computer processor may determine a second angle between thesecond image vector and the gravity vector and assign a second imageidentifier to the second x-ray image based on the second determinedangle. The second x-ray image may be displayed on the display. The stepof displaying the first x-ray image on the display may be performedafter the step of assigning the first image identifier and prior to thestep of acquiring the second x-ray image. The first image identifier maycorrespond with the first x-ray image being one of an anterior-posterior(A-P) x-ray image and a lateral x-ray image of the anatomical structure.The second image identifier corresponds with the second x-ray imagebeing one of another A-P x-ray image and another lateral x-ray image ofthe anatomical structure.

The navigation system may include a memory configured to store a firstpredefined range of angles and a second predefined range of anglesexclusive from the first predefined range of angles. The computerprocessor may then determine whether the first determined angle iswithin the first predefined range of angles and assign the first imageidentifier to the first x-ray image when the first determined angle iswithin the first predefined range of angles. Alternatively, the computerprocessor may determine whether the second determined angle is withinthe second predefined range of angles and assign the second imageidentifier to the second x-ray image when the second determined angle iswithin the second predefined range of angles. The first predefined rangeof angles may be greater than 45° to less than or equal to 135°, and thesecond predefined range of angles may be greater than 0° to less than orequal to 45°, and greater than 135° to less than or equal to 180°.

The tracking element of the tracking device may be a first trackingelement and a second tracking element may be located on a surgicalinstrument. A pose of the surgical instrument may be tracked bydetecting the second tracking element with the tracking sensor. The poseof the surgical instrument may be displayed by overlaying a visualrepresentation of the surgical instrument onto at least one of the firstand second x-ray images on the display with the visual representationappearing from one of at least two different perspectives based on thefirst and second image identifiers. The first and second imageidentifiers are displayed on the display and respectively associatedwith the first and second x-ray images.

The present teachings further include a method for acquiring x-rayimages of an anatomical structure with a C-arm imaging device. Anavigation system may be provided and include a tracking device coupledto the C-arm imaging device which is detectable by a tracking sensor ofa localizer, a gravity vector sensor configured to detect the directiontoward center of Earth gravity regardless of an orientation of thetracking sensor, and a computer processor. A first of the x-ray imageswith the C-arm imaging device may be acquired at an angular position.The tracking sensor may detect a pose of the tracking device as thefirst x-ray image is acquired. The computer processor may be used togenerate a first image vector based on the pose of the tracking device.The computer processor may receive a gravity vector from the gravityvector sensor. The computer processor may determine an angle between thefirst image vector and the gravity vector. The gravity sensor may becoupled to the localizer. The computer processor may determine a firstimage identifier for the first x-ray image based on the determined angleand display the first x-ray image on the display in a manner based onthe image identifier. A second of the x-ray images may be acquired withthe C-arm imaging device. The computer processor may generate a secondimage vector based on the pose of the tracking device and determine anangle between the second image vector and the gravity vector. Thecomputer processor may determine a first image identifier for the firstx-ray image based on the determined angle and update the first x-rayimage on the display with the second x-ray image if the second imageidentifier is the same as the first image identifier. The computerprocessor may determine that the first image identifier and/or thesecond image identifier further identifies the x-ray image as either alateral x-ray image or an anterior-posterior (A-P) x-ray image. Thex-ray image may be identified as the A-P x-ray image if the determinedangle is within a first predefined range of angles or as the lateralx-ray image if the determined angle is within a second predefined rangeof angles exclusive from the first predefined range of angles. The firstpredefined range of angles may be greater than 45° to less than or equalto 135°, and the second predefined range of angles may be greater than0° to less than or equal to 45°, and greater than 135° to less than orequal to 180°. A visual representation of a surgical instrument may beoverlaid onto the x-ray image on the display with the visualrepresentation appearing from one of at least two different perspectivesbased on whether the x-ray image is identified as the lateral x-rayimage or the A-P x-ray image.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingswherein:

FIG. 1 illustrates a perspective view of the surgical navigation system.

FIG. 2 illustrates a display showing an anterior-posterior view and alateral view along with a surgical instrument and its location relativea target bone area.

FIG. 3 shows an x-ray imaging device including a C-arm and a moveableimaging portion, the imaging portion coupled with a tracking device.

FIG. 4A illustrates the tracking device and localizer with the opticaltracking sensor and gravity vector sensor, and the associated anglevectors in a first representative position.

FIG. 4B illustrates the tracking device and localizer with the opticaltracking sensor and gravity vector sensor, and the associated anglevectors in a second representative position.

FIG. 5 shows the process by which the surgical navigation systemdetermines which view to display based on the determined angle.

DETAILED DESCRIPTION

The explanations and illustrations presented herein are intended toacquaint others skilled in the art with the teachings, its principles,and its practical application. Those skilled in the art may adapt andapply the teachings in its numerous forms, as may be best suited to therequirements of a particular use. Accordingly, the present disclosure isnot intended to be exhaustive or limiting. The scope of the teachingsshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles and references,including patent applications and publications, are incorporated byreference for all purposes. Other combinations are also possible as willbe gleaned from the following claims, which are also hereby incorporatedby reference into this written description.

The present teachings generally relate to a surgical navigation systemfor use in surgery. Particularly, the surgical navigation system may beused for pre-operative planning, intraoperative use, or post-operativefollow up. The surgical navigation system may function with an x-rayimaging device to acquire x-ray images of one or more anatomical objectsof interest and display the x-ray images to a surgeon or surgery team.For example, the surgical navigation system may take and display anx-ray image of a particular anatomical feature or region (e.g. knee,spine, ankle, foot, neck, hip, arm, leg, rib cage, hand, shoulder, head,the like, or a combination thereof). The surgical navigation system mayfunction to superimpose an image of surgical instruments over thedisplayed x-ray image of the anatomical feature, displaying the surgicalinstruments relative the anatomical feature. For example, the surgicalnavigation system may superimpose the image of a surgical instrumentrelative to imaged anatomical feature so that the surgeon may observethe relative distance of the surgical instrument and the target portionof the anatomical feature which is to be affected by the surgicalinstrument. The surgical navigation system may function to acquiremultiple x-ray images. For example, a first x-ray image may be acquiredin a first pose, and the surgical navigation system displays that imageat a first orientation corresponding to the position of the C-arm. Asecond x-ray image may then be taken after the first x-ray image. Thesurgical system may then determine whether the image is in the firstpose or a second pose based on information generated by the trackingsensors and a gravity vector sensor. The surgical navigation system mayautomatically correlate the second image with its correct orientation.The surgical navigation system may replace the first image if the imagepose is the same, and/or display the second image in a second posedifferent than the first pose. The surgical navigation system mayautomatically update the displayed images as additional images areacquired at the same positions. The surgical navigation system maycomprise a computer processor connected with an x-ray imaging device, alocalizer, and the gravity vector sensor. The localizer may monitor theposition of an image tracking device located on the imaging portion ofthe x-ray imaging device. The surgical navigation system may beconnected with a display configured to present one or more imagesacquired by the x-ray imaging device.

The surgical navigation system may be connected with an x-ray imagingdevice. The x-ray imaging device may function to acquire images of thepatient or anatomical features of the patient's body. The x-ray imagingdevice may include a structure with an x-ray emitting portion (e.g.,x-ray tube) and an imaging portion (e.g., x-ray detector). The x-rayimaging device may be configured as a C-arm. The C-arm may include thex-ray tube at a first end of the C-arm and the x-ray detector located onthe opposing second end of the C-arm. The x-ray tube and the x-raydetector may be at a fixed distance from each other. An imaging regionmay be defined in the center of the c-shape, between the x-ray tube andthe x-ray imaging portion. A patient or a portion of a patient may belocated in the center section of the C-arm, between the x-ray tube andthe x-ray detector, so that a specific portion of the patient may beimaged. The C-arm may be moved between a plurality of positions. TheC-arm may be rotated about a patient or anatomical feature of interest,tilted relative to a patient or particular anatomical feature, raised,lowered, repositioned, or a combination thereof. During movement, theimaging portion and the x-ray source maintain a fixed relationship,keeping the same distance on the opposite ends of the C-arm.

An image tracking device may be removably coupled with the imagingportion of the C-arm. The image tracking device may function to indicatethe position or pose of the imaging portion of the x-ray imaging device.The image tracking device may be disposed over the imaging portion whileallowing the imaging portion to acquire the desired x-ray images of thepatient or object of interest. The image tracking device may include oneor more tracking elements which may be used in conjunction with alocalizer. The one or more tracking elements may be sensed by thelocalizer so that the localizer can track the position of the one ormore tracking elements, conveying the position of the image trackingdevice to the localizer.

The surgical navigation system may include a plurality of trackingelements. The tracking elements may function to be sensed and tracked bythe localizer. The image tracking device, the one or more surgicalinstruments, the one or more patient trackers, or a combination thereofmay each include at least one of tracking elements. The trackingelements may be any feature or structure adapted to be sensed by thesurgical navigation system with the localizer. In some arrangements, thetracking elements may include an LED, a reflective surface, a reflectivepattern, a magnetic coil, a radio transmitter, and/or an opticallyidentifiable geometric shape that uniquely defines position andorientation perceivable by the localizer.

The surgical navigation system may include the localizer. The localizermay function to monitor and track the image tracking device on theimagining portion of the C-arm, surgical instruments, patient trackers,or a combination thereof. One suitable localizer is the FP6000 trackingcamera manufactured by Stryker Corporation (Kalamazoo, Mich.). Thelocalizer may function to send information regarding the position of thetracking device, surgical instruments, patient tracker, or a combinationthereof to a computer processor. The localizer may include one or moreof the tracking sensors, the gravity vector sensor, or both. Thelocalizer may use an optical means, a magnetic means, a radio frequencymeans, or a combination thereof for monitoring the location of theimagine tracking device, the surgical instruments, the patient tracker,or a combination thereof. The optical means of detection may function inthe visible light spectrum, the infrared spectrum, or both. The magneticmeans of detection may acknowledge and track differences in magneticfields. The radio frequency means of detection may function to trackradio frequencies. The localizer may be in a fixed position or amoveable position. For example, the localizer may be attached to astationary stand and positioned in the surgery room. In another example,the localizer may be located on a moveable base. The localizer may beplaced in any location within the operation room which has a line ofsight to the tracking elements on the image tracking device, thesurgical instruments, the patient tracker, or a combination thereof.

The localizer may include one or more tracking sensors. The trackingsensors may function to identify the position of the image trackingdevice on the imaging portion of the C-arm. The tracking sensors mayfunction to acquire positional information of the image tracking device,the surgical instruments, the patient trackers, or a combinationthereof, communicating the corresponding positional information to thecomputer processor. The tracking sensors may have an optical means, amagnetic means, a radio frequency means, or a combination thereof tosense the position of the image tracking device, the surgicalinstruments, the patient tracker, or a combination thereof at the momentan x-ray image is acquired. The optical means may function in thevisible light spectrum, the infrared spectrum, or both. For example, theone or more tracking sensors may be one or more cameras, such as CCD,CMOS, optical image, or a combination thereof. The magnetic means ofdetection may acknowledge and track differences in magnetic fields. Theradio frequency means may function to track radio frequencies. Thetracking sensor may be positioned in any location which has a line ofsight to the tracking elements on the image tracking device, thesurgical instruments, the patient tracker, or a combination thereof.

The surgical navigation system may track the position and movement ofone or more surgical instruments. The one or more surgical instrumentsmay function to probe, cut, saw, drill, grind, debride, cauterize,probe, the like, or a combination thereof. The surgical instruments maybe handheld, robotic, powered, nonpowered, or a combination thereof. Thesurgical instruments may include at least one tracking element. Thetracking element may be registered with the localizer so that thelocalizer may track the position of the surgical instruments in realtime. The surgical instruments may be tracked and displayed in real timeover the images acquired by the x-ray imaging device so that thelocation of the working end of the surgical instruments relative theanatomical feature is known.

The surgical navigation system may include one or more patient trackerson a patient. The patient tracker may function with the navigationsystem to detect and compensate for movement and deformations during aprocedure, adjusting so that the surgeon and/or surgery team have areal-time location of the surgical instruments, the target anatomicalfeature, or both. The patient tracker may include at least one trackingelement. The patient tracker may be any shape that is suitable to trackmovement and compression of a patient during a procedure. The patienttracker is not limited to a particular shape or form, and may be rigid,flexible, and/or have multiple separate sections. In one example, thepatient tracker has a plurality of tracking elements, such as LEDs,disposed on a flexible substrate having the shape of a generallyrectangular frame with an open window there through that can beremovably secured to the patient's skin with adhesive.

The surgical navigation system may include a gravity vector sensor. Thegravity vector sensor may function to detect the direction toward centerof Earth gravity, regardless of position or orientation. The directiontoward the center of Earth gravity is a gravity vector. The gravityvector sensor determines the gravity vector regardless of the positionof the gravity vector sensor. The gravity vector may be used as areference point to determine the position of another object, since thegravity vector sensor provides the gravity vector which is always towardthe center of Earth gravity. For example, the gravity vector may bereferenced to determine the angular position of the image trackingdevice by comparing the relative position of the image tracking deviceto the gravity vector. The gravity vector sensor may be located anywhereas long as a connection with the computer processor is maintained. Forexample, the gravity vector sensor may be located within the localizer.The gravity vector sensor may be connected with the computer processorthrough a wired connection, a wireless connection, a network, or acombination thereof.

The surgical navigation system may include a computer processor. Thecomputer processor may function to analyze the information received fromthe localizer and the gravity vector sensor. The computer processor mayfunction to determine the pose of one or more images acquired by thex-ray imaging device. The computer processor may function to process thepositional data collected by the localizer with the images acquired bythe x-ray imaging device so that the x-ray images are displayed based onthe sensed position of the image tracking device relative to the gravityvector. The computer processor may receive data from the tracking sensorand the gravity vector sensor. The computer processor may calculate animage vector of the image tracking device received from the trackingsensor within the localizer. The image vector is the angular position ofthe image tracking device on the C-arm of the x-ray imaging device. Thecomputer processor may calculate the sensed position of the imagetracking device at the moment an image is taken by the x-ray imagingdevice by generating the image vector based on the tracking sensors andtracking elements of the image tracking device, and the gravity vectorfrom the gravity vector sensor. The computer processor then calculatinga determined angle which is the angular difference between the perceivedlocation of the image tracking device and the gravity vector. Thecomputer processor may analyze the determined angle in a database or alibrary, and assign an image orientation based on the sensed data fromthe moment the image was acquired by the x-ray imaging device. Thecomputer processor may then send the image capture data to the imagedisplay to be displayed to the surgeon and/or surgery team in theappropriate orientation automatically. The computer processor analyzesand determines the angular position and orientation of each image thex-ray imaging device acquires. The computer processor may automaticallyupdate a displayed image with a subsequently acquired image when thedetermined angle of that image falls within the same predefined rangeangles. The computer processor may further process positional data ofthe surgical instruments, the patient trackers or both. For example, thecomputer processor may display the position of the surgicalinstrument(s) onto a displayed first perspective image, a displayedsecond perspective image, or both simultaneously, showing the positionof the one or more surgical instruments relative the anatomical featureas the surgical instrument is moved during the procedure.

The computer processor may include a memory. The memory may function tohold one or more libraries, databases, lookup tables, or a combinationthereof. The memory may function to store data relating to the positionof the C-arm (image vector), the images taken by the x-ray imagingdevice, the gravity vector value, a first predefined range of angels, asecond predefined range of angles exclusive from the first predefinedrange of angles, a plurality of image identifiers corresponding to theposition of the image tracking device, or a combination thereof. Thememory may be transitory memory, non-transitory memory, or both. In oneexample, the memory includes a first predefined range and a secondpredefined range exclusive of the first predefined range, and thecomputer processor compares the determined angle of the acquired x-rayimage with the first predefined range of angles and the secondpredefined range of angles to determine which predefined range thedetermined angle falls within. Once calculated, the computer processorassigns an image identifier to the x-ray image and shows the x-ray imageon the display in the correct orientation. The memory may includemultiple predefined ranges, each predefined range being exclusive fromeach other. Each of the predefined ranges is associated with an imageidentifier.

The computer processor may assign an image identifier based on thepredefined range which the determined angle falls within. Each of theimage identifiers may function to provide an indication of the one ofthe plurality of angular position at which the x-ray image was acquired.The computer processor may designate a unique image identifier for eachof the plurality of predefined ranges of angles. For example, a firstpredefined range of angles may be greater than 45° to less than or equalto 135° and correspond with an anterior-posterior (A-P) imageidentifier. In another example, the second predefined range of anglesmay be greater than 0° to less than or equal to 45°, and greater than135° to less than or equal to 180° and correspond with a lateral imageidentifier. The image identifier corresponding to the angular positionof the x-ray image may be presented on the display with the x-ray image.

Turning to FIG. 1 , a perspective view of the surgical navigation system10 and the x-ray imaging device 12 are illustrated. The x-ray imagingdevice 12 including a C-arm 14 with an imaging portion 16 and x-ray tube17. Connected with the imaging portion 16 is the tracking device 18. Thetracking device 18 is disposed over the imaging portion 16 of the x-rayimaging device 12 to transmit data relating to the position of theimaging portion 16. The C-arm 14 is shown surrounding a patient P suchthat the imagining portion 16 and the x-ray tube 17 are perpendicular tothe spine of the patient P.

The localizer 30 is connected with moveable arm 36, attaching thelocalizer 30 to the computer processor 38 configured as a moveable unit.The localizer 30 may be placed in any position within the vicinity ofthe surgical procedure and x-ray imaging device 12 to accommodatespacing issues within the surgical area. The localizer 30 is configuredto track the tracking elements 28 of the image tracking device 18 on theimaging portion 16 of the C-arm 14. The localizer 30 tracks the movementof the image tracking device 18 between positions by sensing theposition of the tracking elements 28. As the imaging portion 16 is movedbetween a plurality of positions (See FIGS. 4A and 4B), the localizer 30collects location data, sending the location data of the image trackingdevice 18, as well as the gravity vector data from the gravity vectorsensor 32, to the computer processor 38. The localizer 30 may be furtherconfigured to track a patient tracker 26, for example, the SpineMaskTracker manufactured by Stryker Leibinger GmbH & Co. KG (Freiberg,Germany).

The localizer 30 and display 50 are shown as being located on thecomputer processor 38. In one implementation, the display 50 andlocalizer 30 may be separate structures from the computer processor 38.The display 50 is shown as having two screens, each screen displaying animage. FIG. 2 is a closeup of display 50 with the first image 52 in ananterior-posterior view of the anatomical feature and the surgical tool24, and the second image 54 is in a lateral view of the of the surgicaltool 24 and the anatomical feature, which, in this example, is a portionof the spine of patient P. The first image 52 is displayed with a firstimage identifier 56 indicating “anterior-posterior” and the second image54 shown with the second image identifier 58 indicating “lateral.” Inthe first displayed image 52, the surgical tool 24 is shown at a planecontacting the spine from the A-P view. The second displayed image 54shows the surgical tool 24 contacting the spine from the lateral view.By providing both the A-P view and the lateral view, the surgeon canascertain the position of the surgical tool 24 relative to theanatomical feature. It is contemplated that the image identifier may notbe displayed on the display 50, but rather exist as data assigned to theimages, which may be utilized by the computer processor 38 forsubsequent aspects of the image routine.

FIG. 3 is a perspective view of the image tracking device 18 disposedover the imaging portion 16 of the C-arm. The image tracking device 18includes tracking elements 28 which are configured to be tracked by thelocalizer 30. The localizer 30 as pictured in FIG. 1 , optically tracksthe tracking elements 28 of the image tracking device 18 as the imagingportion 16 of the C-arm 14 is moved from position to position. When theimaging portion 16 of the C-arm 14 is moved from position to positionand taking x-ray images, the localizer 30 determines the coordinates ofthe pose of the tracking device 18 at the moment each of the x-rayimages are acquired. The localizer 30 sends the coordinates of the poseto the computer processor 38 to be analyzed with the gravity vector 42.

Turning to FIGS. 4A, 4B, and 5 , the localizer 30 is shown with trackingsensors 34 and gravity vector sensor 32. The tracking sensors 34 areconfigured to optically track tracking elements 28 on the image trackingdevice 18 on the imaging portion 16 of the C-arm 14. The localizer 30sends the relative position of the image tracking device 18 and thegravity vector data from the gravity vector sensor 32 to the computerprocessor 38. The computer processor 38 then calculates an image vector41 relative the gravity vector 42. The gravity vector sensor 32 may bewithin the localizer 30, however, it is contemplated that the gravityvector sensor 32 may be located separate of the localizer 30. Thecomputer processor 38 analyzes the pose of the image tracking device 18as determined by the tracking sensors 34 of the localizer 30 relative tothe gravity vector 42 as determined by the gravity vector sensor 32 andcalculates the determined angle (α) 44. The computer processor 38 usesthe determined angle 44 to ascertain which pose the imaging portion 16of the C-arm 14 was in when the x-ray image was taken.

The computer processor 38 includes a memory coupled with the computerprocessor. The memory is configured to store a plurality of predefinedrange of angles, with each predefined range of angles being exclusive.In this example, the memory includes at least a first predefined rangeof angles and a second predefined range of angles exclusive from thefirst predefined range of angles.

In one example, the computer processor 38 determines between two poseswhich the imaging portion 16 of the C-arm 14 can be in when an x-rayimage is taken. The computer processor 38 determines whether the imagingportion 16 of the image tracking device 18 is in the A-P pose or thelateral pose. The A-P pose is associated with the angular differencebetween the image vector 41 of the image tracking device 18 and thegravity vector 42 calculated by the computer processor 38 for adetermined angle 44 of 0°<α≤45° and 135°<α≤180°. The lateral pose isassociated with the angular difference between the image vector 41 ofthe tracking device 18 and the gravity vector 42 calculated by thecomputer processor 38 for a determined angle 44 of 45°<α≤135°.

Once the computer processor 38 calculates and determines thecorresponding pose of the x-ray imaging device 16, the computerprocessor may automatically display the x-ray image 52, 54 on thedisplay 50 with its associated image identifier. When the x-ray imagingdevice acquires several x-ray images which fall within the samepredefined range of angles, the computer processor automatically updatesthe x-ray image displayed with the most current image acquired. Forexample, the x-ray imaging device takes a first A-P image and a secondA-P image after the first A-P image, the second A-P image will replacethe first A-P image on the display automatically. This may improveworkflow between preoperative planning and intraoperative imaging sincean operator will not have to signal the surgical navigation system whichimage(s) is going to be updated with another x-ray image.

The surgical navigation system 10 also provides for a visualrepresentation of a surgical instrument 24. The visual representation ofthe surgical instrument 24 is overlaid onto the displayed image 52, 54,showing the visual representation of the surgical instrument appearingfrom one of at least two different perspectives based on the imageidentifier. The display is configured to display the x-ray image 52, 54with image identifiers 56, 58 corresponding to the angular position atwhich the x-ray image was acquired.

The present disclosure is not intended to be exhaustive or limit theinvention to any particular form. The terminology which has been used isintended to be in the nature of words of description rather than oflimitation. Many modifications and variations are possible in light ofthe above teachings and the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A surgical navigation system for use with anx-ray imaging device configured to acquire an x-ray image of ananatomical structure at one of a plurality of angular positions relativeto a direction toward center of Earth gravity, the system comprising: alocalizer unit comprising a tracking sensor and a gravity vector sensor,the tracking sensor and the gravity vector sensor mounted to thelocalizer unit, wherein the gravity vector sensor is configured todetect the direction toward center of Earth gravity regardless of anorientation of the tracking sensor; a tracking device configured to becoupled to the x-ray imaging device so as to be movable with movement ofthe x-ray imaging device between the plurality of angular positions, thetracking device comprising a tracking element detectable by the trackingsensor; a computer processor operatively coupled to the localizer unit;and a display coupled to the computer processor, wherein the computerprocessor configured to implement an imaging routine comprising:receiving tracking data from the tracking sensor and a gravity vectorfrom the gravity vector sensor; generating an image vector based on thetracking data with the image vector being indicative of the one of theplurality of angular positions at which the x-ray image was acquired;determining an angle between the image vector and the gravity vector;and assigning a first image identifier to the x-ray image based on thedetermined angle, the first image identifier configured to provide anindication of the one of the plurality of angular position at which thex-ray image was acquired, wherein the system is configured to displaythe x-ray image with the first image identifier; updating the x-rayimage on the display with a second x-ray image on the display responsiveto the second x-ray image being assigned a second image identifier thesame as the first image identifier, the second image identifier based ona second determined angle between a second image vector being indicativeof one of the plurality of angular positions at which the second x-rayimage was acquired, and the gravity vector.
 2. The system of claim 1,further comprising memory coupled to the computer processor andconfigured to store a first predefined range of angles and a secondpredefined range of angles exclusive from the first predefined range ofangles, wherein the imaging routine further comprises: receiving thefirst and second predefined ranges of angles from the memory;determining whether the determined angle is within the first predefinedrange of angles or the second predefined range of angles; and assigningthe first image identifier to the x-ray image when the determined angleis within the first predefined range of angles and not within the secondpredefined range of angles.
 3. The system of claim 2, wherein the firstpredefined range of angles is greater than 450 to less than or equal to1350, and wherein the second predefined range of angles is greater than00 to less than or equal to 450, and greater than 1350 to less than orequal to
 1800. 4. The system of claim 3, wherein the first imageidentifier is a lateral image identifier configured to be displayedalong with the x-ray image to provide the indication that the x-rayimage is a lateral x-ray image of the anatomical structure.
 5. Thesystem of claim 1, wherein the computer processor is configured todisplay a visual representation of a surgical instrument onto the x-rayimage on the display with the visual representation appearing from oneof at least two different perspectives based on the image identifier. 6.A method for acquiring x-ray images of an anatomical structure with aC-arm imaging device and identifying the x-ray images on a display,wherein a navigation system is provided and includes a localizer unitincluding a tracking sensor connected to the localizer unit and agravity vector sensor mounted to the localizer unit and configured todetect a direction toward center of Earth gravity regardless of anorientation of the tracking sensor, a tracking device coupled to theC-arm imaging device and including a tracking element detectable by thetracking sensor, and a computer processor, said method comprising:acquiring a first x-ray image with the C-arm imaging device at a firstangular position, wherein the tracking sensor detects a first pose ofthe tracking device as the first x-ray image is acquired; generatingwith the computer processor a first image vector based on the first poseof the tracking device; generating a gravity vector based on the gravityvector sensor; determining with the computer processor a first anglebetween the first image vector and the gravity vector; assigning withthe computer processor a first image identifier to the first x-ray imagebased on the first determined angle; displaying the first x-ray image onthe display; acquiring a second x-ray image with the C-arm imagingdevice at a second angular position different than the first angularposition, wherein the tracking sensor detects a second pose of thetracking device as the second x-ray image is acquired; generating withthe computer processor a second image vector based on the second pose ofthe tracking device; determining with the computer processor a secondangle between the second image vector and the gravity vector; assigningwith the computer processor a second image identifier to the secondx-ray image based on the second determined angle; updating the x-rayimage on the display with the second x-ray image on the displayresponsive to the second x-ray image being assigned a second imageidentifier the same as the first image identifier.
 7. The method ofclaim 6, wherein the tracking element of the tracking device is a firsttracking element, said method further comprising: providing a surgicalinstrument, and a second tracking element coupled to the surgicalinstrument; tracking a pose of the surgical instrument by detecting thesecond tracking element with the tracking sensor; and overlaying avisual representation of the surgical instrument onto at least one ofthe first and second x-ray images on the display with the visualrepresentation appearing from one of at least two different perspectivesbased on the first and second image identifiers.
 8. The method of claim6, wherein the first image identifier corresponds with the first x-rayimage being one of an anterior-posterior (A-P) x-ray image and a lateralx-ray image of the anatomical structure, and wherein the second imageidentifier corresponds with the second x-ray image being one of anotherA-P x-ray image and another lateral x-ray image of the anatomicalstructure.
 9. The method of claim 6, wherein the navigation systemincludes memory configured to store a first predefined range of anglesand a second predefined range of angles exclusive from the firstpredefined range of angles, said method further comprising: determiningwith the computer processor whether the first determined angle is withinthe first predefined range of angles; assigning the first imageidentifier to the first x-ray image when the first determined angle iswithin the first predefined range of angles; determining with thecomputer processor whether the second determined angle is within thesecond predefined range of angles; and assigning the second imageidentifier to the second x-ray image when the second determined angle iswithin the second predefined range of angles.
 10. The method of claim 9,wherein the first predefined range of angles is greater than 450 to lessthan or equal to 1350, and wherein the second predefined range of anglesis greater than 00 to less than or equal to 450, and greater than 1350to less than or equal to
 1800. 11. The method of claim 6, wherein thestep of displaying the first x-ray image on the display is performedafter the step of assigning the first image identifier and prior to thestep of acquiring the second x-ray image.